1. Field of the Invention
The present invention provides a transceiver for receiving and transmitting data over a network, and a method for testing the same. Specifically, the present invention provides a physical layer transceiver having a built-in-self-test (BIST) device that allows for variation of a pulse density/width of a network data signal, and offset variation of a reference clock signal for improved testing of the transceiver.
2. Background Art
Physical layer transceiver circuits are commonly used in network (e.g., LAN) communication applications. As known in the art, transceivers are devices that typically include digital logic, an analog receiver for receiving network data and an analog transmitter for transmitting network data. Due to their relatively simple design, it was easy to test early stage transceivers. Specifically, the digital logic was tested via Level-Sensitive Scan Design (LSSD) techniques, the transmitter was tested through a series of DC parametric measurements, while the receiver was tested through a latched receiver test. Various methods of testing transceivers are generally shown in U.S. Pat. Nos. 5,337,316, 5,402,440, 5,648,972 and 5,676,588.
As transceivers have become more complex, however, accurate and inexpensive ways to test the transceivers have become scarce. In particular, the complexity of the receiver portion of the transceivers have typically grown at a rate faster than the digital logic or the transmitter portions. Thus, while the logic and transmitter portions can continue to be tested via LSSD and parametric procedures, the receivers require more complex testing measures.
Heretofore, attempts have been made to provide improved testing procedures for such transceivers. One such attempt is shown in U.S. Pat. No. 6,298,458 to Cranford et al, herein incorporated by reference. In Cranford et al., a built-in-self-test (BIST) device was provided to provide improved transceiver testing. Specifically, the BIST device generated both a data signal representative of data being transmitted over a network, and a control signal for impairing characteristics of the data signal. The data signal and control signal were passed to the transmitter, which generated an output signal having data according to the data signal and impaired characteristics according to the control signal. The output signal was then forwarded to the receiver, which attempted to reconstruct the original data signal. By analyzing the reconstructed data signal, the BIST device could detect erroneous performance by the transceiver.
The BIST device of Cranford et al. allows for basic functions of the transceiver to be tested by mimicking simple problems such as elongated transit paths and signal slurring. However, system level problems such as control over the signal outputted to the receiver and reference clock signal jitter could not be tested. Specifically, controlling the pulse density/width of the data signal outputted to the receiver allows for a more thorough test (e.g., clock recovery) of the transceiver to be performed. Moreover, by varying the offset of the reference clock signal, the capability of the transceiver to accommodate jitter can be tested.
In view of the foregoing, there exists a need for a transceiver for receiving and transmitting data over a network. Moreover, a need exists for a method for testing such a transceiver. Still yet, a need exists for a transceiver having an improved BIST device that allows for variation of pulse density/width of a network data signal, and offset variation of the reference clock signal embedded within the network data signal.